Process integration of a single chip three axis magnetic field sensor

ABSTRACT

A semiconductor process integrates three bridge circuits, each include magnetoresistive sensors coupled as a Wheatstone bridge on a single chip to sense a magnetic field in three orthogonal directions. The process includes various deposition and etch steps forming the magnetoresistive sensors and a plurality of flux guides on one of the three bridge circuits for transferring a “Z” axis magnetic field onto sensors orientated in the XY plane.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. application Ser. No.12/751,927 filed 31 Mar. 2010.

FIELD

The present invention generally relates to the field ofmagnetoelectronic devices and more particularly to a process forintegrating on a single chip CMOS-compatible magnetoelectronic fieldsensors used to sense magnetic fields in three orthogonal directions.

BACKGROUND

Sensors are widely used in modern systems to measure or detect physicalparameters, such as position, motion, force, acceleration, temperature,pressure, etc. While a variety of different sensor types exist formeasuring these and other parameters, they all suffer from variouslimitations. For example, inexpensive low field sensors, such as thoseused in an electronic compass and other similar magnetic sensingapplications, often comprise anisotropic magnetoresistance (AMR) baseddevices. In order to arrive at the required sensitivity and reasonableresistances that match well with CMOS, the sensing units of such sensorsare generally on the order of square millimeters in size. For mobileapplications, such AMR sensor configurations are costly, in terms ofexpense, circuit area, and power consumption.

Other types of sensors, such as Hall effect sensors, giantmagnetoresistance (GMR) sensors, and magnetic tunnel junction (MTJ)sensors, have been used to provide smaller profile sensors, but suchsensors have their own concerns, such as inadequate sensitivity andbeing effected by temperature changes. To address these concerns, MTJsensors and GMR sensors have been employed in a Wheatstone bridgestructure to increase sensitivity and to eliminate temperature dependentresistance changes. Many magnetic sensing technologies are inherentlyresponsive to one orientation of applied field, to the exclusion oforthogonal axes. Indeed, two-axis magnetic field sensors have beendeveloped for electronic compass applications to detect the earth'sfield direction by using a Wheatstone bridge structure for each senseaxis.

For example, Hall sensors are generally responsive to out-of-plane fieldcomponents normal to the substrate surface, while thin-filmmagneto-resistive sensors, including most AMR, GMR, and MTJ sensordevices, are responsive to in-plane applied magnetic fields. Utilizingthese responsive axes, development of a small footprint three axissensing solution typically involves a multi chip module with one or morechips positioned at orthogonal angles to one another. Formagnetoresistive sensors, the orthogonal in-plane components may beachieved with careful sensor design, but the out-of-plane response iscommonly garnered through vertical bonding or solder reflow to contact asecondary chip that has been mounted vertically. As the size of thevertically bonded chip is typically dominated by the pad pitch asdetermined from the handling constraints, such a technique results in alarge vertical extent of the finished package, high die and assemblycosts, and makes chip scale packaging difficult and costly, asthrough-chip vias must be incorporated.

Accordingly, a need exists for an inexpensive fabrication process forpackaging a low cost single chip magnetic sensor having a reduced diefootprint and that is responsive to an applied magnetic field in threedimensions. There is also a need for a three-axis sensor that can beefficiently and inexpensively constructed as an integrated circuitstructure for use in mobile applications. There is also a need for animproved magnetic field sensor and fabrication to overcome the problemsin the art, such as outlined above. Furthermore, other desirablefeatures and characteristics of the present invention will becomeapparent from the subsequent detailed description and the appendedclaims, taken in conjunction with the accompanying drawings and thisbackground.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will hereinafter be described inconjunction with the following drawing figures, wherein like numeralsdenote like elements, and

FIG. 1 illustrates a three-axis magnetic field sensor structure whichuses differential sensors formed from three bridge structures with MTJsensors that may be integrated in accordance with exemplary embodiments;

FIGS. 2-9 are a partial cross section of the Z axis bridge structure ofFIG. 1 as it progresses through the process integration in accordancewith a first exemplary embodiment;

FIGS. 10A, 10B, and 10C are flow charts of the steps of the processintegration in accordance with the first exemplary embodiment of FIGS.2-9;

FIG. 11 is a partial cross section of a modification of FIG. 4 inaccordance with a second exemplary embodiment;

FIG. 12 is a partial cross section of a modification of FIG. 8 inaccordance with a second exemplary embodiment;

FIG. 13 is a partial cross section of a modification of FIG. 6 inaccordance with a third exemplary embodiment;

FIG. 14 is a view of flux lines as calculated by finite elementsimulation of two of the four Z-axis sensors of FIG. 9; and

FIG. 15 is a graph illustrating the Z sensitivity expressed as apercentage of the X sensitivity for a single (not differentially wired)MTJ sense element as a function of the cladding to sensor spacing.

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the drawings have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements for purposes of promoting andimproving clarity and understanding. Further, where consideredappropriate, reference numerals have been repeated among the drawings torepresent corresponding or analogous elements.

SUMMARY

A method of integrating a single chip three-axis magnetic field elementhaving a film plane with an in-plane field sensitivity and out-of-planethin-film flux guides configured to respond to magnetic field componentsperpendicular to the film plane includes etching a first and a secondplurality of trenches within a first dielectric layer, each trench ofthe first and second plurality of trenches having a bottom and a side;depositing a first material on the sides of each of at least the firstplurality of trenches, the first material having a high magneticpermeability; depositing a second material in the first plurality oftrenches and a third material within the second plurality of trenches,the third material being electrically conductive; depositing a seconddielectric layer over the first dielectric layer and the first andsecond plurality of trenches; forming a first plurality of conductivevias through the second dielectric layer to the third material in afirst portion of the second trenches; forming a first plurality ofthin-film magneto-resistive field sensor elements upon the seconddielectric layer positioned adjacent to the sides of the first pluralityof trenches, one each of the first plurality of thin-filmmagneto-resistive field sensor elements electrically coupled to one ofthe first plurality of vias; and depositing a third dielectric layerover the second dielectric layer and the first plurality of thin-filmmagneto-resistive field sensor elements.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding background or the following detaileddescription.

Through the integration of high aspect ratio vertical bars (flux guides)of a magnetically permeability material, typically having a permeabilityof greater than 100 and more preferably having a permeability of greaterthan 1000 such as nickel iron alloys (NiFe), whose edges terminate inclose proximity to opposed edges and opposite sides of a magnetic senseelement, a portion of the vertical (Z-axis) field can be brought intothe plane of the sense element (the X-Y plane). Permeability is thedegree of magnetization that a material obtains in response to anapplied magnetic field. These flux guides serve to capture magnetic fluxfrom the Z component of an applied magnetic field, and in so doing, bendthe field lines in a substantially horizontal manner near the ends ofthe flux guides. Through asymmetric positioning of the flux guides,e.g., the flux guide segment above the left edge of sense elements intwo legs of the four legs of a Wheatstone bridge, and the flux guideabove the right edge of sense elements in the other two legs, thehorizontal components may act in an opposite directions for the twopairs of legs resulting in a strong differential signal. A field appliedin the X or Y direction will project equally on all four legs of thebridge and, with the proper sense element design, can be subtracted outfrom and not contribute to the final sensor signal. Separate bridges areincluded elsewhere on the magnetic sensor chip for determining the X andY components of the magnetic signal, and in this manner, a field withcomponents in all three spatial orientations can be accuratelydetermined by a single chip magnetoresistive sensing module, forexample, based on magnetic tunnel junction (MTJ) sense elements. FiniteElement Method (FEM) simulations have shown that a pair of high aspectratio flux guides, e.g., 25 nm wide by 500 nm high and extending severalmicrons in the third direction, when optimally positioned will provide asignal on an individual element that is about 80% of the of the signalmeasured from an in plane (x axis) field of the same strength.Additional signal may be obtained through closer proximity of the fluxguide to the sensor, increases in the flux guide height, and additionalshaping of the guide geometry. One example is to add horizontal segmentsparallel to the sense element which extend over the edges of the senseelement. Other examples are to form a U which is placed with theinterior horizontal segment aligned with the outer edge of the senseelement, angled termination of the vertical segments to extend the fluxguide partially in the plane of the sense element, and a similarlyplaced box structure. These geometries serve to further enhance thehorizontal component of the guided flux and move it to a more centralregion of the sensor. A structure with individual 25 nm wide verticalbars utilized as flux guides is tolerant to overlay errors and producesan apparent x to z field conversion (for a differentially wiredWheatstone bridge) at the rate of 2.5% for a misalignment of 85 nmbetween a single flux guiding layer and the sense layer.

The flux guiding layer may be formed from layers typically used in themagnetic random access memory (MRAM) process flow, during which bit anddigit lines cladded with a high permeability magnetic material (such asNiFe-based or CoFe-based alloys) on three sides, referred to herein as aflux guide, are used to increase the field factors present to reduce thecurrent needed to switch the memory storage element. In the sensorapplication, similar processes may be used with the optional additionalstep of sputtering out the bottom of the digit line in order to removeany cladding present on the trench's bottom. Modifications may be madeto the process flow so that the height and width of the cladding usedfor flux guiding are at optimum values instead of the 500 nm and 25 nm,respectively, that are used in the exemplary process described above.

A method and apparatus are subsequently described in more detail forproviding multi-axis pinning on a bulk wafer which may be used to forman integrated circuit sensor with different reference layers havingthree different pinning directions, two of which are substantiallyorthogonal, that are set with a single pinning material deposition andbulk wafer setting procedure. As a preliminary step, a stack of one ormore layers of ferromagnetic and antiferromagnetic materials are etchedinto shaped reference layers having a two-dimensional shape with a highaspect ratio, where the shape provides a distinction for the desiredmagnetization direction for each reference layer. Depending on thematerials and techniques used, the final magnetization direction may beoriented along the short axis or the long axis of the shaped layer. Forexample, if the reference layer is formed with a slightly imbalancedsynthetic anti-ferromagnet (SAF) patterned into micron-scale dimensions,the magnetization will direct along the short axis. As will beappreciated by those skilled in the art, the SAF embodiment provides anumber of benefits related to the use of pinned-SAF reference layers inmagnetoelectronic devices. In other embodiments, by controlling thethicknesses of the pinned and fixed layers and the in-plane spatialextent of the patterned structure, the final magnetization may bedirected along the long axis. Using shape anisotropy, differentmagnetization directions are induced in the reference layers by heatingin the presence of an orienting field that is aligned between thedesired magnetization directions for the reference layers. In selectedembodiments, the reference layers are heated sufficiently to reduce thematerial component of the anisotropy and allow the shape and externalfield to dominate the magnetization direction. In this manner, once theorienting field is removed, the shape anisotropy directs themagnetization in the desired direction. Upon removing the orientingfield, the magnetizations of the reference layers relax to follow theshape of the reference layers so as to induce a magnetization that isaligned along the desired axis of the shaped reference layer. Anoptional compensating field may be applied to help induce orthogonality,and the reference layers are then heated to above the phase transitiontemperature of the antiferromagnetic pinning layers. For example, if tworeference layers are shaped to have longer dimensions which areperpendicular to one another, then the induced magnetizations for thetwo reference layers will be approximately perpendicular to one another.A small compensation angle may be introduced so that while the long axisof the two reference layers are not perpendicular, the resultant inducedmagnetizations are substantially perpendicular to one another.

FIG. 1 is a magnetic field sensor 100 formed with first, second, andthird differential sensors 101, 111, 121 for detecting the componentdirections of an applied field along a first axis 120 (e.g., the y-axisdirection), a second axis 110 (e.g., the x-axis direction), and a thirdaxis 130 (e.g., the z-axis direction), respectively. The z-axisdirection is represented as a dot and cross-hairs as going either intoor out of the page on which FIG. 1 is situated. Exemplary embodiments ofthe first and second sensors 101, 111 are described in detail in U.S.patent application Ser. No. 12/433,679. As depicted herein, each sensor101, 111, 121 is formed with unshielded sense elements that areconnected in a bridge configuration. Thus, the first sensor 101 isformed from the connection of a plurality of sense elements 102-105 in abridge configuration over a corresponding plurality of reference layers106-109, where each of the reference layers 106-109 is magnetized in thex-axis direction. In similar fashion, the second sensor 111 is formedfrom the connection of a plurality of sense elements 112-115 in a bridgeconfiguration over a corresponding plurality of reference layers 116-119that are each magnetized in the y-axis direction that is perpendicularto the magnetization direction of the reference layers 106-109.Furthermore, the third sensor 121 in the same plane as the first andsecond sensors 101, 111 is formed from the connection of a plurality ofsense elements 122-125 in a bridge configuration over a correspondingplurality of reference layers 126-129 that are each magnetized in thexy-axis direction that is at about 45 degrees to the magnetizationdirection of the reference layers 106-109 and 116-119. In certainembodiments, reference direction of the third sensor 121 may lie alonganother axis. In the depicted bridge configuration 101, the senseelements 102, 104 are formed to have a first easy axis magnetizationdirection and the sense elements 103, 105 are formed to have a secondeasy axis magnetization direction, where the first and second easy axismagnetization directions are orthogonal with respect to one another andare oriented to differ equally from the magnetization direction of thereference layers 106-109. As for the second bridge configuration 111,the sense elements 112, 114 have a first easy axis magnetizationdirection that is orthogonal to the second easy axis magnetizationdirection for the sense elements 113, 115 so that the first and secondeasy axis magnetization directions are oriented to differ equally fromthe magnetization direction of the reference layers 116-119. In thethird bridge configuration 121, the sense elements 122 123,124, and 125all have an easy axis magnetization direction that is orthogonal to thereference magnetization direction of the reference layers 126, 127, 128,and 129. The third bridge configuration 121 further includes flux guides132-135 positioned adjacent to the right edge of sense elements 122-125,and flux guides 136-139 positioned adjacent to the left edge of senseelements 122-125, respectively. Flux guides 132,137, 134, and 139 arepositioned above sense elements 122-125, and flux guides 136, 133, 138,and 135 are positioned below sense elements 122-125. The positioning ofthese flux guides 132-139 is subsequently described in more detail inFIG. 2. In the depicted sensors 101, 111, 121 there is no shieldingrequired for the sense elements, nor are any special reference elementsrequired. In an exemplary embodiment, this is achieved by referencingeach active sense element (e.g., 102, 104) with another active senseelement (e.g., 103, 105) using shape anisotropy techniques to establishthe easy magnetic axes of the referenced sense elements to be deflectedfrom each other by approximately 90 degrees for the X and Y sensors, andreferencing a sense element that responds in an opposite manner to anapplied field in the Z direction for the Z sensor. The Z sensorreferencing will be described in more detail below. The configurationshown in FIG. 1 is not required to harvest the benefits of the thirdsensor 121 structure described in more detail in FIGS. 2-9, and is onlygiven as an example.

By positioning the first and second sensors 101, 111 to be orthogonallyaligned, each with the sense element orientations deflected equally fromthe sensor's pinning direction and orthogonal to one another in eachsensor, the sensors can detect the component directions of an appliedfield along the first and second axes. Flux guides 132-139 arepositioned in sensor 121 above and below the opposite edges of theelements 122-125, in an asymmetrical manner between legs 141, 143 andlegs 142, 144. As flux guides 132, 134 are placed above the senseelements 122, 124, the magnetic flux from the Z-component of an externalmagnetic field may be guided by the flux guides 132 and 134 into the xyplane along the right side and cause the magnetization of sense elements122 and 124 to rotate in a first direction towards a higher resistance.Similarly, the magnetic flux from the Z field may be guided by the fluxguides 133 and 135 into the xy plane along the right side of the senseelement and cause the magnetization of sense elements 123 and 125 torotate in a second direction, opposite from the first direction towardsa lower resistance, as these flux guides are located below the senseelements 123, 125. Thus, the sensor 121 can detect the componentdirections of an applied field along the orthogonal (Z) axis. Althoughin the preferred embodiment, the flux guides are in a plane orthogonalto the plane of the field sensor, the flux guides will still function ifthe angle they make with the sensor is not exactly 90 degrees. In otherembodiments, the angle between the flux guide and the field sensor couldbe in a range from 45 degrees to 135 degrees, with the exact anglechosen depending on other factors such as on the ease of fabrication.

As seen from the foregoing, a magnetic field sensor may be formed fromdifferential sensors 101, 111, 121 which use unshielded sense elements102-105, 112-115, and sense elements 122-125 with guided magnetic fluxconnected in a bridge configuration over respective pinned, orreference, layers 106-109, 116-119, and 126-129 to detect the presenceand direction of an applied magnetic field. With this configuration, themagnetic field sensor provides good sensitivity, and also provides thetemperature compensating properties of a bridge configuration.

The bridge circuits 101, 111, 121 may be manufactured as part of anexisting MRAM or thin-film sensor manufacturing process with only minoradjustments to control the magnetic orientation of the various sensorlayers and cross section of the flux guiding structures. See forexample, U.S. Pat. No. 6,174,737. Each of the reference layers 106-109,116-119, and 126-129 may be formed with one or more lower ferromagneticlayers, and each of the sense elements 102-105, 112-115, 122-125 may beformed with one or more upper ferromagnetic layers. An insulatingtunneling dielectric layer (not shown) may be disposed between the senseelements 102-105, 112-115, 122-125 and the reference layers 106-109,116-119, and 126-129. The reference and sense electrodes are desirablymagnetic materials whose magnetization direction can be aligned.Suitable electrode materials and arrangements of the materials intostructures commonly used for electrodes of magnetoresistive randomaccess memory (MRAM) devices and other magnetic tunnel junction (MTJ)sensor devices are well known in the art. For example, reference layers106-109, 116-119, and 126-129 may be formed with one or more layers offerromagnetic and antiferromagnetic materials to a combined thickness inthe range 10 to 1000 Å, and in selected embodiments in the range 250 to350 Å. In an exemplary implementation, each of the reference layers106-109, 116-119, and 126-129 is formed with a single ferromagneticlayer and an underlying anti-ferromagnetic pinning layer. In anotherexemplary implementation, each reference layer 106-109, 116-119, and126-129 includes a synthetic anti-ferromagnetic stack component (e.g., astack of Cobalt Iron (CoF), Ruthenium (Ru) and Cobalt Free Boron (CoFeB)which is 20 to 80 Å thick, and an underlying anti-ferromagnetic pinninglayer that is approximately 200 Å thick. The lower anti-ferromagneticpinning materials may be re-settable materials, such as IrMn and FeMn,though other materials, such as PtMn can be used which are not readilyre-set at reasonable temperatures. As formed, the reference layers106-109, 116-119, and 126-129 function as a fixed or pinned magneticlayer when the direction of its magnetization is pinned in one directionthat does not change during normal operating conditions. As disclosedherein, the heating qualities of the materials used to pin the referencelayers 106-109, 116-119, and 126-129 can change the fabrication sequenceused to form these layers.

One of each of the sense elements 102-105, 112-115, 122-125 and one ofeach of the reference layers 106-109, 116-119, 126-129 form a magnetictunnel junction (MTJ) sensor. For example, for bridge circuit 121, senseelement 122 and reference layer 126 form an MTJ sensor 141. Likewise,sense element 123 and reference layer 127 form an MTJ sensor 142, senseelement 124 and reference layer 128 form an MTJ sensor 143, and senseelement 125 and reference layer 129 form an MTJ sensor 144.

The reference layers 106-109, 116-119, and 126-129 may be formed with asingle patterned ferromagnetic layer having a magnetization direction(indicated by the arrow) that aligns along the long-axis of thepatterned reference layer(s). However, in other embodiments, thereference layer may be implemented with a synthetic anti-ferromagnetic(SAF) layer which is used to align the magnetization of the referencelayer along the short axis of the patterned reference layer(s). As willbe appreciated, the SAF layer may be implemented in combination with anunderlying anti-ferromagnetic pinning layer, though with SAF structureswith appropriate geometry and materials that provide sufficiently strongmagnetization, the underlying anti-ferromagnetic pinning layer may notbe required, thereby providing a simpler fabrication process with costsavings.

The sense elements 102-105, 112-115, 122-125 may be formed with one ormore layers of ferromagnetic materials to a thickness in the range 10 to5000 Å, and in selected embodiments in the range 10 to 100 Å. The upperferromagnetic materials may be magnetically soft materials, such asNiFe, CoFe, Fe, CoFeB and the like. In each MTJ sensor, the senseelements 102-105, 112-115, 122-125 function as a sense layer or freemagnetic layer because the direction of their magnetization can bedeflected by the presence of an external applied field, such as theEarth's magnetic field. As finally formed, sense elements 102-105,112-115, 122-125 may be formed with a single ferromagnetic layer havinga magnetization direction (indicated with the arrows) that aligns alongthe long-axis of the patterned shapes.

The reference layers 106-109, 116-119, 126-129 and sense elements102-105, 112-115, 122-125 may be formed to have different magneticproperties. For example, the reference layers 106-109, 116-119, 126-129may be formed with an anti-ferromagnetic film exchange layer coupled toa ferromagnetic film to form layers with a high coercive force andoffset hysteresis curves so that their magnetization direction will bepinned in one direction, and hence substantially unaffected by anexternally applied magnetic field. In contrast, the sense elements102-105, 112-115, 122-125 may be formed with a magnetically softmaterial to provide different magnetization directions having acomparatively low anisotropy and coercive force so that themagnetization direction of the sense electrode may be altered by anexternally applied magnetic field. In selected embodiments, the strengthof the pinning field is about two orders of magnitude larger than theanisotropy field of the sense electrodes, although different ratios maybe used by adjusting the respective magnetic properties of theelectrodes using well known techniques to vary their composition.

The reference layers 106-109, 116-119, 126-129 in the MTJ sensors areformed to have a shape determined magnetization direction in the planeof the reference layers 106-109, 116-119, 126-129 (identified by thevector arrows for each sensor bridge labeled “Pinning direction” in FIG.1). As described herein, the magnetization direction for the referencelayers 106-109, 116-119, 126-129 may be obtained using shape anisotropyof the pinned electrodes, in which case the shapes of the referencelayers 106-109, 116-119, 126-129 may each be longer in the pinningdirection for a single reference layer. Alternatively, for a pinned SAFstructure, composed of two or more ferromagnetic layers separated bycoupling spacer layers, the ferromagnetic layers may be shorter alongthe pinning direction. In particular, the magnetization direction forthe pinned layers 106-109, 116-119, 126-129 may be obtained by firstheating the shaped reference layers 106-109, 116-119, 126-129 in thepresence of a orienting magnetic field which is orientednon-orthogonally to the axis of longest orientation for the shapedreference layers 106-109, 116-119, 126-129 such that the appliedorienting field includes a field component in the direction of thedesired pinning direction for the reference layers 106-109, 116-119,126-129. The magnetization directions of the reference layers arealigned, at least temporarily, in a predetermined direction. However, byappropriately heating the reference layers during this treatment andremoving the orienting field without reducing the heat, themagnetization of the reference layers relaxes along the desired axis oforientation for the shaped reference layers 106-109, 116-119, 126-129.Once the magnetization relaxes, the reference layers can be annealedand/or cooled so that the magnetic field direction of the referenceelectrode layers is set in the desired direction for the shapedreference layers 106-109, 116-119, 126-129.

The structure of the sensor devices 141-144 of the third bridge circuit121 include the reference layers 126-129, the sense elements 122-125,and the flux guides 132-139, all formed within the dielectric material140 and integrated with the process disclosed herein. The flux guide 136has an end positioned below an edge of the sensor element 122. The fluxguides 133 and 138 have ends positioned below edges of the sensorelements 123 and 124, respectively. The flux guide 135 has an endpositioned below an edge of the sensor element 125. The flux guides 132and 137 have ends positioned above edges of the sensor elements 122 and123, respectively, and the flux guides 134 and 139 have ends positionedabove edges of the sensor elements 124 and 125, respectively. The endsof the flux guides may be brought as close as possible to the sensorelements, with a preferable spacing of less than or equal to 250 nmbetween the two. The sense elements are brought as close as possible forthe tightest density array, preferably less than 2.5 um apart.

The exemplary embodiments described herein may be fabricated using knownlithographic processes as follows. The fabrication of integratedcircuits, microelectronic devices, micro electro mechanical devices,microfluidic devices, and photonic devices involves the creation ofseveral layers of materials that interact in some fashion. One or moreof these layers may be patterned so various regions of the layer havedifferent electrical or other characteristics, which may beinterconnected within the layer or to other layers to create electricalcomponents and circuits. These regions may be created by selectivelyintroducing or removing various materials. The patterns that define suchregions are often created by lithographic processes. For example, alayer of photo resist material is applied onto a layer overlying a wafersubstrate. A photo mask (containing clear and opaque areas) is used toselectively expose this photo resist material by a form of radiation,such as ultraviolet light, electrons, or x-rays. Either the photo resistmaterial exposed to the radiation, or that not exposed to the radiation,is removed by the application of a developer. An etch may then beapplied to the layer not protected by the remaining resist, and when theresist is removed, the layer overlying the substrate is patterned.Alternatively, an additive process could also be used, e.g., building astructure using the photo resist as a template.

Various illustrative embodiments of the process integration will now bedescribed in detail with reference to the accompanying figures. Whilevarious details are set forth in the following description, it will beappreciated that the present invention may be practiced without thesespecific details, and that numerous implementation-specific decisionsmay be made to the invention described herein to achieve the devicedesigner's specific goals, such as compliance with process technology ordesign-related constraints, which will vary from one implementation toanother. While such a development effort might be complex andtime-consuming, it would nevertheless be a routine undertaking for thoseof ordinary skill in the art having the benefit of this disclosure. Inaddition, selected aspects are depicted with reference to simplifiedcross sectional drawings without including every device feature orgeometry in order to avoid limiting or obscuring the present invention.It is also noted that, throughout this detailed description,conventional techniques and features related to magnetic sensor designand operation, Magnetoresistive Random Access Memory (MRAM) design, MRAMoperation, semiconductor device fabrication, and other aspects of theintegrated circuit devices may not be described in detail herein. Whilecertain materials will be formed and removed to fabricate the integratedcircuit sensors as part of an existing MRAM fabrication process, thespecific procedures for forming or removing such materials are notdetailed below since such details are well known and not considerednecessary to teach one skilled in the art of how to make or use thepresent invention. Furthermore, the circuit/component layouts andconfigurations shown in the various figures contained herein areintended to represent exemplary embodiments of the invention. It shouldbe noted that many alternative or additional circuit/component layoutsmay be present in a practical embodiment.

Referring to FIGS. 2 and 10A, 10B, and 10C, and in accordance with anexemplary embodiment of the integration process, a first etch stop layer204 is deposited 1002 over a substrate 202. A first dielectric layer 206is deposited 1004 over the first etch stop layer 204 and a plurality offirst trenches 208 are etched 1006 through the first dielectric layer206 to the first etch stop layer 204. A magnetically permeabilitymaterial 212, having a permeability greater than 100 and preferablygreater than 1000, such as a NiFe or CoFeB, is deposited 1008 within thefirst plurality of trenches 208 and on the first dielectric layer 206.The magnetically permeable material 212 is back sputtered away 1010(FIG. 3) from the bottom of the first plurality of trenches 208 and fromthe top of the first dielectric layer 206, resulting in a magneticallypermeable layer 214 (also referred to as cladding, or flux guide, orflux concentrators) on the sides 216 of the first plurality of trenches208. Furthermore, the step of forming the magnetically permeablematerial on the sides 216 of the first plurality of trenches 208 may beshortened in time or eliminated to allow some of the magneticallypermeable material to remain on the bottom of the first and secondplurality of trenches 208, 222 and the first region 224, therebyproviding a “U” shaped flux guide upon removal of magnetically permeablematerial from the top surface of the first dielectric layer 206 in asubsequent step, for example by polishing.

A second dielectric layer 218 is then deposited 1012 on the etch stoplayer 204 in the trenches 208 and on the dielectric layer 206. If thedeposition process is conformal, the second dielectric layer 218 willalso cover the flux guides 216.

A second plurality of trenches 222 (FIG. 4) and a first region 224 areetched 1014 through the first dielectric layer 206 to the first etchstop layer 204 and, preferably, a conductive material 226, e.g., copper,is deposited 1016 in the first and second plurality of trenches 208, 222and the first region 224 and polished 1018 to provide a smooth surface228. Alternatively, a metal such as aluminum could be deposited and thensubtractively patterned to form conductive lines separated by the firstand second plurality of trenches 208, 222 after which the magneticallypermeable cladding might be applied to the sides of the trench on theremaining aluminum, for example by sputter deposition. The first region224 may be a trench formed orthogonal to the second plurality oftrenches 222. In this case, the filled trenches 208 are subtractivelypatterned metal. Alternatively, the first plurality of trenches 208 maybe filled with a dielectric material. Furthermore, the conductivematerial 226 may be deposited as two separate layers, a first layerwithin the first plurality of trenches 208 and a second layer within thefirst region 224 and second plurality of trenches 222.

Magnetically permeable material 215 (see FIG. 11) may also be formed inthe second plurality of trenches 222 and the region 224 at the same timeas the flux guides 214 are formed.

Referring to FIG. 5, a second etch stop layer 232 is deposited 1020 onthe surface 228 and a third dielectric layer 234 is deposited over thesecond etch stop layer 232. A first plurality of vias 236 are etched1024 through the third dielectric 234 and the second etch stop layer 232to the conductive material 226 in a portion of the second plurality oftrenches 222, and a conductive material 238 is placed 1026 within thefirst plurality of vias 236. A first plurality of tunnel junctionsensors, each including the sense element 123 and the reference layer127 (FIG. 1), are formed 1028 on the third dielectric layer 234, witheach of the reference layers 127 making contact with one of the firstplurality of the conductive material 238 within the first plurality ofvias 236. A second plurality of tunnel junction sensors, each includingthe sense element 123 and the reference layer 127 are formed 1028 on thethird dielectric layer 234 and over the region 206. Dielectric layer 242is then deposited 1030 over the first plurality of tunnel junctionsensors and third dielectric layer 234.

Referring to FIG. 6, a third etch stop layer 246 is deposited 1032 overthe fourth dielectric layer 242 and a fifth dielectric layer 248 isdeposited 1034 over the third etch stop layer 246. Third and fourthplurality of trenches 252, 254 are etched 1036 through the fifthdielectric layer 248 and the third etch stop layer 246, with one each ofthe third plurality of trenches 252 formed over one each of the senseelements 123, while the fourth plurality of trenches 254 are formed overthe first and second trenches 208, 222 not having a sense element 123therebetween. A magnetically permeable material 256 is deposited 1038within the third and fourth plurality of trenches 252, 254 and on thefifth dielectric layer 248.

Referring to FIG. 7, the magnetically permeable material 256 isbacksputtered away 1040 (FIG. 10B) from the bottom of the third andfourth plurality of trenches 252, 254, resulting in a magneticallypermeable layer 258 on the sides 262 (also referred to as cladding, fluxguide, or flux concentrators) of the third and fourth plurality oftrenches 252, 254. A sixth dielectric layer 264 is deposited 1042 on thefourth dielectric 242 in the trenches 252, 254 and on the fifthdielectric layer 248.

Referring to FIG. 8, a fifth plurality of trenches 272 are etched 1044through the sixth and fifth dielectric layers 264, 248, the third etchstop layer 246, and a portion of the fourth dielectric layer 242 to thesense elements 123, while a trench 274 is etched through the sixth andfifth dielectric layers 264, 248, the third etch stop layer 246, and aportion of the fourth dielectric layer 242, all over the first region224. The fifth plurality of trenches 272 and the trench 274 may alsocontain flux concentrators 259 as shown in FIG. 12. These fluxconcentrators 259 would preferably be formed in the same manner and withthe same process as the flux concentrators 258. A further etch isperformed 1046 within the trench 274 to form a second via 276 throughthe fourth and third dielectric layers 242, 234 and the etch stop layer232 to the conductive material 226, and within the trenches 254 to formthird vias 277. At the same time vias 277 are etched as well. Aconductive material 282, e.g., copper, is then filled 1048 within thethird, fourth, and fifth trenches and the unique trench 274 and polished1050 to form the smooth surface 278. This conductive material also fillsvias 276 and 277.

A fourth etch stop layer 283 is deposited 1052 on the surface 278 (FIG.9), and a seventh dielectric layer 284 is deposited 1054 on the fourthetch stop layer 283. A sixth and seventh plurality of trenches 286, 288are etched 1056 in the seventh dielectric layer 284 to the fourth etchstop layer 283. Another etch is performed 1058 in the sixth and one ofthe seventh plurality of trenches 286, 288 to form a third plurality ofvias 292 between the sixth and the one of the seventh plurality oftrenches 286, 288 to the fourth plurality of trenches 254 and the trench274, respectively. A conductive material 292 such as copper is filled1060 within the sixth and seventh trenches 286, 288 and the thirdplurality of vias 292. The filled sixth plurality of trenches is aconductor (e.g., a stabilization layer) to provide a stabilizationfield. The structure 200 is then passivated 1062 in a well known manner.Alternatively, Al metal may be deposited before the dielectric 284 isdeposited and then etched to form the patterned top metal, and then adielectric 284 may be deposited over top.

In another exemplary embodiment (FIG. 13), the trenches 253 (FIG. 12)are formed at the same time as third and fifth trenches 252, 272 (seeFIG. 8), and all regions have magnetically permeability flux guidesdeposited and sputtered. This simplifies the process by removing theseparate dielectric deposition and photo step.

In another exemplary embodiment (FIG. 11), the trenches 224, 222 (FIG.12) are formed at the same time as trenches 208 (see FIG. 8), and allregions have magnetically permeability flux guides deposited andsputtered. This further simplifies the process by removing the separatedielectric deposition and photo step.

In another exemplary embodiment (FIG. 13), after deposition of the thirdetch stop layer 246, contact to the sensor is made through deposition ofa thin dielectric layer (not shown) formed on the third etch stop layer246, and subsequent etching of a via that stops on the upper electrodeof the sense layer 123. At the same time this via 245 is etched, aslightly deeper via 247 is etched that stops on the lower electrode 127beside the patterned sense layer 123 creating a contact path to thereference layer 127. Both vias are filled as a Ta, TaN, Ti or othermetal local interconnect layer 249 is deposited. This local interconnect249 is then patterned, and dielectric 248 is deposited over top. Theupper flux guides trenches (253) may be fabricated as described above ,but are physically offset from the sense layer 123 and do not makeelectrical contact to it. This allows for more freedom in sensor layoutand design.

In yet another embodiment, after deposition of the local interconnectlayer 249 mentioned in the preceding paragraph, the upper flux guides251 may be left out entirely. An etch stop 283 and dielectric layer 285are deposited and trenches 288 are etched. Permeable magnetic materialmay be deposited and sputtered in these trenches 288, and then they arefilled with a metal, for example, copper, and CMP polished. Thestructure is then passivated. A metal layer, preferably Al, below thedielectric 202 may be patterned into electrically conductive lines whichconnect with a metal layer (preferably Al) spaced above the metal 292 bya dielectric layer (not shown) and also patterned into electricallyconductive lines for imposing a self test field upon the sensor.

FIG. 14 is a view of flux lines as calculated by finite elementsimulation of sensor devices 141, 142 of FIG. 1 with a magnetic field inthe Z direction 130 imparted upon the devices. Finite Element Method(FEM) modeling shows the resultant magnetic flux lines 160, exhibiting acomponent in the plane of the sensor. Sensor device 141 is representedby flux guides 132 and 136 on opposed ends of the sensing element 122.Sensor device 142 is represented by flux guides 133 and 137 on opposedends of the sensing element 123. Stated otherwise, sensing element 122extends from flux guides 132 and 136, and sensing element 123 extendsfrom flux guides 133 and 137. The component of an external magneticfield along the Z axis 130 interacts with the flux guides 132, 136, 133,and 137 to produce an asymmetric response in the sensing elements 122,123 along the X-axis 120 as indicated by the arrows 170. In this manner,for an applied field in the Z direction 130 directed towards the bottomof the page, the magnetization of sense element 122 rotates away fromthe pinning direction (and to higher resistance) of the reference layer126, while the magnetization of sense element 123 rotates towards thepinning direction (and to lower resistance) of reference layer 127. Fora field in the X direction 120, both elements 122, 123 show inducedmagnetization in the same direction (towards higher or lowerresistance). Therefore, by wiring MTJ elements 141, 142 in a Wheatstonebridge for differential measurement and subtracting the resistances ofMTJ devices 141, 142, the X field response is eliminated and twice the Zfield response is measured.

FIG. 15 is a graph showing the Z/X sensitivity ratio versus thecladding/sensor spacing for a 25 nm wide, 500 nm tall vertical segmentsplaced above and below the sense element. The Z/X sensitivity ratioincreases, to about 75 percent, as the cladding is brought to 25nanometers of distance. Additional factors may be gained through crosssectional changes such as those highlighted above, or through aspectratio improvements in the flux guide, for example, making the guidetaller will linearly increase the Z/X sensitivity ratio. Therefore, itis important to bring the flux guide as close as possible to the senseelement, and increase its height as much as is possible withoutadversely impacting the magnetic microstructure.

A manner to increase the flux guide 214 height in an exemplaryembodiment is to etch the trench 208 (FIG. 2) in dielectric 206, depositthe permeable magnetic material 212, fill the trenches with copper, andthen perform a chemical metal polish to expose the surface. This sameprocess is repeated again on top of the filled trenches 208 so that theflux guides from the two (or more) repeats of this process flow directlyalign vertically. An optional dielectric spacer layer (not shown) may bedeposited between the multiple flux guides 302, 304 to magneticallydecouple them from one another so as to reduce the propensity formagnetic domains to form at the microstructure formed at the interfacebetween the two vertically aligned flux guides 302, 304. This processmay also be utilized for the flux guides 258.

Furthermore, vias may be formed below the dielectric 204 and coveredwith magnetically permeability material 212 and filled at the same timeas the sides 216 of the first plurality of trenches 208. This processforms taller flux guides where the sides of the vias are aligned withthe sides of the first plurality of trenches 216.

Although the described exemplary embodiments disclosed herein aredirected to various sensor structures and methods for making same, thepresent invention is not necessarily limited to the exemplaryembodiments which illustrate inventive aspects of the present inventionthat are applicable to a wide variety of semiconductor processes and/ordevices. Thus, the particular embodiments disclosed above areillustrative only and should not be taken as limitations upon thepresent invention, as the invention may be modified and practiced indifferent but equivalent manners apparent to those skilled in the arthaving the benefit of the teachings herein. For example, the relativepositions of the sense and pinning layers in a sensor structure may bereversed so that the pinning layer is on top and the sense layer isbelow. Also the sense layers and the pinning layers may be formed withdifferent materials than those disclosed. Moreover, the thickness of thedescribed layers may deviate from the disclosed thickness values.Accordingly, the foregoing description is not intended to limit theinvention to the particular form set forth, but on the contrary, isintended to cover such alternatives, modifications and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims so that those skilled in the art shouldunderstand that they can make various changes, substitutions andalterations without departing from the spirit and scope of the inventionin its broadest form.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention, it beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set forth in the appendedclaims.

The invention claimed is:
 1. A method of manufacturing an integratedthree axis magneto-resistive sensor, the method comprising: etching aplurality of first trenches in a first insulating material disposed on asubstrate, wherein each first trench includes a plurality of side walls;forming first flux guides in the plurality of first trenches bydepositing a magnetically permeable material on at least two side wallsof each of the plurality of first trenches; depositing a secondinsulating material in each of the first plurality of trenches, whereinthe second insulating material is deposited on the first insulatingmaterial and adjacent to the first flux guides; forming a firstplurality of magneto-resistive sensor elements on the second insulatingmaterial, wherein each sensor element of the first plurality ofmagneto-resistive sensor elements is juxtaposed to and laterally offsetfrom an associated first flux guide; forming a first bridge circuit byelectrically interconnecting the magneto-resistive sensor elements ofthe first plurality of magneto-resistive sensor elements; forming asecond plurality of magneto-resistive sensor elements on the secondinsulating material; forming a second bridge circuit by electricallyinterconnecting the magneto-resistive sensor elements of the secondplurality of magneto-resistive sensor elements; forming a thirdplurality of magneto-resistive sensor elements on the second insulatingmaterial; forming a third bridge circuit by electrically interconnectingthe magneto-resistive sensor elements of the third plurality ofmagneto-resistive sensor elements; and depositing a third insulatingmaterial on or over the first, second, and third pluralities ofmagneto-resistive sensor elements, wherein the first second, and thirdpluralities of magneto-resistive sensor elements are formed in a plane.2. The method of claim 1, wherein forming each of the first plurality ofmagneto-resistive sensor elements on the second insulating materialincludes forming a first reference layer having a first pinningdirection, wherein forming each of the second plurality ofmagneto-resistive sensor elements on the second insulating materialincludes forming a second reference layer having a second pinningdirection, and wherein forming each of the third plurality ofmagneto-resistive sensor elements on the second insulating materialincludes forming a third reference layer having a third pinningdirection.
 3. The method of claim 1, wherein forming eachmagneto-resistive sensor element of the first, second, and thirdpluralities of magneto-resistive sensor elements includes: forming areference layer; forming an intermediate layer on the reference layer;and forming a sensing layer on the intermediate layer, wherein formingthe reference layer of each magneto-resistive sensor element of thefirst plurality of magneto-resistive sensor elements includes forming afirst reference layer having a first pinning direction, wherein formingthe reference layer of each magneto-resistive sensor element of thesecond plurality of magneto-resistive sensor elements includes forming asecond reference layer having a second pinning direction which isdifferent from the first pinning direction, and wherein forming thereference layer of each magneto-resistive sensor element of the thirdplurality of magneto-resistive sensor elements includes forming a thirdreference layer having a third pinning direction which is different fromthe first and second pinning directions.
 4. The method of claim 3,wherein the intermediate layer is an insulating layer.
 5. The method ofclaim 3, wherein forming the reference layer of each magneto-resistivesensor element of the first, second, and third pluralities ofmagneto-resistive sensor elements includes: forming an antiferromagneticpinning layer; and forming a ferromagnetic layer on theantiferromagnetic pinning layer.
 6. The method of claim 3, whereinforming the reference layer of each magneto-resistive sensor element ofthe first, second, and third pluralities of magneto-resistive sensorelements includes: forming a synthetic antiferromagnetic stack.
 7. Themethod of claim 1, wherein the magnetically permeable material includesat least one of nickel, iron, and cobalt.
 8. The method of claim 1,wherein forming each magneto-resistive sensor element of the first,second, and third pluralities of magneto-resistive sensor elementsincludes: forming a reference layer; forming a third insulating materialon the reference layer; and forming a sensing layer on the thirdinsulating material.
 9. The method of claim 1, wherein forming the firstflux guides in the plurality of first trenches includes: depositing themagnetically permeable material into each first trench of the pluralityof first trenches; and back sputtering at least a portion of themagnetically permeable material from a bottom of each first trench ofthe plurality of first trenches, and leaving the magnetically permeablematerial on the at least two side walls of each first trench of theplurality of first trenches.
 10. The method of claim 1, wherein formingthe first flux guides in the plurality of first trenches includes:depositing one or more layers of at least one of nickel, iron, cobalt,and alloys thereof into each first trench of the plurality of firsttrenches.
 11. The method of claim 1, wherein forming the first fluxguides in the plurality of first trenches includes: providing one ormore layers of at least one of nickel, iron, cobalt, and alloys thereofon the at least two side walls of each first trench of the plurality offirst trenches.
 12. The method of claim 1, further including: depositinga conductive material in the plurality of first trenches, on the secondinsulating material, and adjacent to the first flux guides.
 13. Themethod of claim 1, further including: etching a plurality of secondtrenches in the third insulating material, wherein each second trench ofthe plurality of second trenches includes at least two side walls,wherein each second trench is juxtaposed to and laterally offset from anassociated sensor element of the first plurality of magneto-resistivesensor elements; forming second flux guides in the plurality of secondtrenches, wherein each second flux guide includes a second magneticallypermeable material disposed on the at least two side walls of anassociated second trench; and depositing a fourth insulating material onthe third insulating material and the second flux guides.
 14. The methodof claim 13, wherein the second magnetically permeable material includesat least one of nickel, iron, cobalt, and alloys thereof.
 15. The methodof claim 13, wherein forming the second flux guides in the plurality ofsecond trenches includes: depositing the second magnetically permeablematerial into each second trench of the plurality of second trenches;and back sputtering at least a portion of the second magneticallypermeable material from the bottom of each second trench of theplurality of second trenches, and leaving the second magneticallypermeable material on the at least two side walls of each second trenchof the plurality of second trenches.
 16. The method of claim 13, whereinforming the second flux guides in the plurality of second trenchesincludes: depositing one or more layers of at least one of nickel, iron,cobalt, and alloys thereof into each second trench of the plurality ofsecond trenches.
 17. The method of claim 13, wherein forming the secondflux guides in the plurality of second trenches includes: providing oneor more layers of at least one of nickel, iron, cobalt, and alloysthereof on the at least two side walls of each second trench of theplurality of second trenches.
 18. The method of claim 13, furthercomprising: forming a stabilization layer over a portion of the secondplurality of trenches.
 19. The method of claim 18, wherein thestabilization layer includes copper.
 20. The method of claim 1, furthercomprising: forming a plurality of conductive lines upon the thirdinsulating layer.
 21. The method of claim 1, wherein at least one of thefirst plurality of magneto-resistive sensor elements includes a magnetictunnel junction.